Double resonance oscillator



Dec. 3, 1940- w. VAN B. ROBERTS DOUBLE RESONANCE OSCILLATOR Filed April 27. 1938 4' 9mm Mi unnnulvl lunurr INVENTOR. WALTER VAN 8. ROBERTS ATTORNEY.

Patented Dec. 3, 1940 UNITED STATES DOUBLE} RESONANCE osorLLA'ron.

Walter van B. Roberts, Princeton, N. J., assignor to Radio Corporation of America, acorpcration of Delaware Application April 27, 1938. Serial N0. 204,597

12 Claims.

My present invention relates to oscillation generation systems of the type characterized by both circuit resonance and electron oscillation resonance, and which I prefer to call double resonance oscillators.

The chief object of the present invention is to provide means for adjusting the relative phase of the electronic and the circuit oscillations to an optimum value.

A particular object is to provide a vacuum tube oscillation generator delivering power from a pair of electrodes to a resonant tank circuit, and having connections for deriving from this tank circuit and impressing upon electrons in the tube 15 an electric field of optimum phase for producing a resonance vibration of the electrons within the tube such as are requisite for the generation of oscillations by the production of suitably timed pulses of secondary emission current to one of the aforesaid electrodes.

In the accompanying drawing wherein like elements are designated by like reference numerals:

Fig. 1 shows one form of the invention in which circuit provision is made for adjusting to its optimum value the phase relation between oscillations in the output circuit and the oscillatory electronic field employed to cause vibration of electrons within the tube;

Fig. 1a shows a similar arrangement, but with a simplified electrode structure;

Fig. 2 shows a modified form of the invention wherein phase displacement between the voltage on the field electrodes and the voltage on the output electrodes is produced by physical separation of these electrodes of the leads thereto; and

Fig. 3 is another modification ofthe arrangement of Fig. 1, having a hot cathodefor supplying electrons to be brought into vibration.

Referring to Fig. 1, there is shown a cross section of an evacuated tube I constructed in accordance with the invention, together with suitable external connections for the production of oscillations. A coil 2 is provided for producing a constant magnetic field longitudinal of the tube for constraining electrons to vibrate parallel to the axis of the tube. Coil 2 may be omitted if the electron system is constructed and operated in accordance with principles known in the art of electron gun devices so as suitably to direct the motion of electrons; but, if employed, coil 2 is connected to a source of direct voltage [6 of suitable magnitude. An apertured electrode 3 is maintained at a positive potential with respect to a reference point, indicated by the ground symbol, by means of a source 4 of direct potential.

Electrode 3 is the attracting center of force through which electrons vibrate back and forth under the influence of its attraction with a frequency depending upon the voltage of source 4. Perforated electrodes 5 are the field producing 5 electrodes Whose alternating potential diiference acts upon or accelerates the vibrating electrons between them; and plate electrodes 6 are the output electrodes to which pulses of secondary emission current flow when impacted by electrons. 10 Plates 6 emit "secondary electrons when impacted by primary electrons and are connected together through a resonant circuit comprising, coil 1 shunted by variable'condenser 8 and are maintained at a suitable direct potential by connection from the center of coil 1 to ground through direct voltage source 9. Coil l is coupled to coil lo, the latter of which is shunted by variable condenser II, and the terminals of coil II] are connected to electrodes 5, while the center of coil I0 is grounded. Grid electrodes l2 are employed between field electrodes 5 and plates 6 and are connected to ground through direct voltage sources l3, which are so poled as to maintain said grids sufficiently positive relative to ground so as to attract away from plates 6 the secondary electrons emitted therefrom.

The operation of the circuit may be explained most simply by assuming that a single electron is liberated in the space between the electrodes 5, while at the same time circuit 1, 8 is shock excited by some external means not shown. The liberated electron starts vibrating to and fro about the attracting center ring-like electrode 3 with a frequency the same as the natural frequency of the resonant circuit 1, 8, if source 4 is adjusted to the proper voltage. The voltage on electrodes 5 produced by the coupling between circuits 1, 8 and 10, II, has its phase adjusted by proper adjustment of condensers 8 and II and by correct choice of the polarity of the coupling between coils and i0 so that the oscillatory field between electrodes 5 is in phase with the velocity of the electron, and thus increases the amplitude of oscillation of the electron at the expense of 5 oscillatory energy in the external resonant circuits. A very slight increase in kinetic energy of the electron results in its vibration amplitude becoming suiiicient for it to pass through the openings of one of the electrodes 5 and the adjacent grid l2, and to impact upon corresponding plate 6, with the resulting liberation of a number of secondary electrons. At the instant of impact, neglecting the time of-transit-from electrode 5 to plate 6, the potential of electrode 5is zero, while the potential of the impacted plate 6 is maximum and positive if the phase relations are adjusted as described above. Since the liberation of several electrons from plate 6 at the instant when plate 6 is most positive represents a pulse of energy into circuit 1, 8, it is seen that the oscillations originally assumed will be re-enforced. The secondary electrons so produced, except a few that may strike electrodes 3, 5 or [2, are then swung back through the tube to the other end where the same sequence of events takes place, but on a larger scale, since more electrons are involved. This building up process will, of course, reach a limit where space charge forces an increasing number out of their longitudinal paths to be taken up by one or another of the positive electrodes. The essential feature of the system is that the potential of the electrodes 5 which build up the electron vibration amplitude is in phase with the velocity of the electron cloud, while the potential of the output electrodes 6 is in phase with the displacement of the electrons. These relations insure the most efficient building up of oscillatory energy in the oscillating group of charges and also the greatest efficiency in the conversion of this energy into output energy in the resonant circuit 1, 8. The ultimate sources of energy are, of course, the sources 4 and I3, which in the steady state draw electrons to electrodes 3 and 12 as fast, on the average, as they are liberated from plates 6, and the ultimate utilization circuit, i. e., the load, is preferably coupled to coil 1 in each of the figures, as specifically shown in Figs. 1 and 1a by the coil l9.

Under ideal conditions as explained, there should be a 90 phase shift between the output voltage electrodes 6 and the voltage fed. back to electrodes 5, and such a shift is inherently produced by the use of a pair of circuits tuned to resonance, as shown, but it will be understood that any suitable phase adjusting means may be employed for adjusting the phase shift of the voltage feed-back to electrodes 5, and that in practice, for a given voltage of source 4, the optimum adjustment of output circuit tuning and phase of feed-back voltage, as well as the voltage of source 9, will be found experimentally, as in the case of any other type of oscillator. It was also assumed that at least. one electron was liberated by some means as a starting point for the'building up of an oscillating charge within the tube. This assumption isrealized in practice, since there are always some gas molecules in the best vacuum, and cosmic rays or radio-active material or the like are always present to ionize them.

Electrodes 6 will, of course, preferably be treated to promote secondary emission, while the other electrodes may be treated to prevent it, except that in some cases it may be preferable to make electrodes 5 also capable of secondary emission, in order to assist in or entirely provide for the preliminary electron multiplication.

Fig. 1a is a modification of Fig. 1, in which the field electrodes 5 are relied upon for electron multiplication, as well as for building up oscillatory energy of the charge. A magnetic field coil, such as coil 2 of Fig. 1, may be used for the same purpose as there stated, but for simplicity, this coil is omitted from the diagram of Fig. 1a, as well as the source 9 which is not absolutely necessary. The essential departure in Fig. 1a. is within the tube itself, where circular field electrodes 5' are surrounded by annular output or plate electrodes 6', each of which is preferably in the same-plane as the adjacent electrode 5',

except for edge portions bent to overlap the field electrodes 5, so as to prevent electrons from passing between the two electrodes 5 and 6' without striking either. The action of Fig. 1a, which is a little different from Fig. 1, is as follows: Voltage across resonant circuit It, I l of the same frequency as that of an electron vibrating about electrode 3, and in phase with the velocity of the oscillating electron, increases the electrons amplitude of vibration until it strikes electrode 5, which in this modification of the present invention is made secondary emissive and causes the ejection of a number of secondary electrons. Since these leave electrode 5 at the instant its potential is zero, no pulse of energy flows into or out of circuit IE3, H at this instant, although, of course, energy had previously been taken from circuit Hi, II for increasing the energy of the electronic vibration. The secondary electrons are then swept over to the other electrode 5, where further multiplication of the vibrating charge occurs. By successive impacts the oscillating charge soon builds up to the point where it spreads out and begins to impact upon electrodes 6. Due to the natural 90 difference in phase between voltages across the two coupled resonant circuits l, 8 and Ill, ll however, the impacts on. each of the electrodes 6 occur when its potential is positive and maximum, thus delivering a pulse of energy to circuit 1, B, as explained in connection with Fig. 1. This energy is more than sufficient to supply the voltage originally assumed across, circuit ill, so that the oscillations. build up as described previously. It. will be noted that in Fig. la electrodes 5' provide both the required electron multiplication and the accelerating field, while electrodes 6 are relied upon only for energy deliever to circuit 1, 8 as the secondary electrons from 6' are not further utilized and,v being liberated so far off the axis of the tube, are taken up by electrode 3. However, as in Fig. 1, a feature of the arrangement is the use of two sets of electrodes, one having a voltage. phase most. suitable to the acceleration. of oscillating charges and the other a phase best adapted for the absorption of power from secondary emission pulses.

Fig. 2 obtains similar results to the preceding arrangements by the use of a modified evacuated tube I, resembling tube I of Fig. 1,. except. that plates 6 are spaced sufliciently far from electrodes 5. so that the time of flight from electrode 5- to electrode 6 is approximately three-fourths of a cycle of the generated oscillations. Thus, even if electrodesi and. 6' have potentials of similar phase, charges passing through 5 at the instant the potential of 5 is zeroimpact upon 5. when its potential ispositive andv maximum, so that the same benefitsiofv optimum. phase of voltage on 5 for acceleration of charges and optimumphase of voltage one for energy absorptionare. realized as in the previous arrangements. Electrode 6. is, of course, treated to emit secondary electrons. Furthermore, it will be noted that a. difference between the-lengths.of, the lead Wires from. coil 1 to electrodes 5 and 6 also affects the relative phase of potentials on electrodes Sand 6, and this complication must be taken into account in the caseof ultra high frequencies where, indeed, the benefits of the invention may be very simply obtained by a suitable and convenient dimensioning of these lead wires to electrodes lland 6. Slidable shorting bars l1 may afford a convenient means to adjustthe length of the'leads l8 fromcoil I to electrodes 6; In Fig; 2 it is preferable to make electrodes 5-seconda'ryemissive and of suflicient cross section to act as the electron multiplier electrodes aswell as field electrodesfthus leaving to electrodes 6 only the energy absorbing function, as was the casein Fig. 1a.

Fig. 3 shows still another embodiment of the invention, here'a hot cathode I4 is provided in the axis of a concentric cylindrical structure including in" sequence a grid 3' functioning-as a center of attraction and held at a positive potential by connection to a battery 4,'an accelerating electrode 5 energized from resonant circuit W, H, and an output secondary emissive electrode 6 connected to a resonant output circuit 1', 8'. Resonant circuits 1, 8 and IO', H are coupled together. Grid 5 is also maintained at a positive potential by battery l5, so as to insure that secondary electrons from plate 6 do not fall back on plate 6. This makes unnecessary the addition of another positive electrode between 5 and 6. l

The operation of Fig. 3 is generally similar to that previously described, except that as is known in the art, a cloud of electrons oscillating about positive grid 3 may be produced in the presence of a hot cathode without the provision of secondary emission multiplication. Such oscillations are often referred to as Barkhausen- Kurz oscillations. Regardless of the means employed for building it up, the objects of my invention are attained if, in connection with such an oscillating cloud, two sets of electrodes 5 and 6 are used, having such different voltage phases as are best suited on the one hand to the increasing of the amplitude of the electronic vibrations and on the other hand to the absorption of power by pulses of secondary emission current.

While I have described a variety of embodiments of my invention, it will be apparent that the broad principles common to these various embodiments may be employed in many modified forms, and I therefore do not consider the invention to be limited except in accordance with the following claims. For example, although I have shown tuned circuits employing concentrated reactances, I am not limited thereby but can equally employ tuned circuits in the form of resonant lines, or other oscillatory systems.

What is claimed is:

1. In an electron multiplier structure having an accelerating electrode and an output electrode wherein an electron cloud is oscillated against and away from said output electrode to liberate energy by secondary emission therefrom upon impact therewith, the method of producing sustained oscillations which comprises absorbing useful power from a part of the energy so liberated, producing from said liberated energy a voltage in phase with the position of said cloud, shifting the phase of said last named voltage by substantially 90 to produce a quadrature voltage, and supplying said quadrature voltage to said accelerating electrode in phase with the velocity of said electron cloud, whereby oscillations are sustained,

2. In combination, a vacuum tube containing a secondary emissive output electrode and a circuit therefor, an accelerating electrode, a resonant load circuit connected in the output circuit, means for setting up electronic oscillations within said tube, and a feed back circuit for impressing voltage of adjustable phase derived from said output circuit upon said accelerating electrode, whereby said oscillations are increased in amplitude to cause pulses of electronic current to said output electrode and thereby to sustain oscillations in said output circuit.

3. A generator of electronic oscillations comprising, in combination, an apertured central electrode, a pair of accelerating electrodes on each side thereof, a secondary emission electrode on each side of said central electrode and located on that side of its adjacent accelerating electrode which is away from said central electrode, all of said electrodes being in an evacuated envelope, an output circuit connected between said secondary emission electrodes, means for maintaining said central electrode at a potential relatively high compared to said other electrodes, and means for impressing between said accelerating electrodes a voltage derived from said output circuit but shifted in phase with respect to voltage between said secondary emission electrodes.

4. A generator of electronic oscillations comprising, in combination, a first pair of electrodes in the form of grids on opposite sides of an apertured central electrode, a second pair of grids similarly located on opposite sides of but spaced farther away from said central electrode, a resonant circuit coupled between said first pair of grids, means for applying a positive potential to said central electrode relative to said first pair of grids, means for applying positive potentials to said second pair of grids relative to said first pair of grids, a pair of opposed electrodes capable of emitting secondary electrons at a ratio greater than unity also located on opposite sides of said central electrode but at a farther distance from said central electrode than said second pair of grids, and a resonant circuit con-.

nected between said pair of secondary emissive electrodes, said two resonant circuits being coupled together to provide feed-back coupling and tunable for adjusting relative phase of voltage in said circuits.

5. In combination, a pair of opposed grid electrodes capable of emitting secondary electrons at a ratio greater than unity, a second pair of opposed electrodes, a circuit of variable electrical length coupled between each electrode of said first pair and the adjacent electrode of the second pair, means for producing an oscillating cloud of electrons between said first pair of electrodes, the distance between each electrode of said second pair and the adjacent electrode of said first pair being so chosen that the time of flight of an electron therebetween is an appreciable portion of a cycle of the generated oscillations.

6. In combination, a pair of opposed grid electrodes capable of emitting secondary electrons at a ratio greater than unity, a second pair of opposed electrodes, means for producing an oscillating cloud of electrons between said electrodes, and means for feeding back energy from said second pair of electrodes to said first pair in optimum phase to sustain oscillations.

7. In combination, a pair of opposed grid electrodes capable of emitting secondary electrons at a ratio greater than unity, a second pair of opposed secondary emissive electrodes, means for producing an oscillating cloud of electrons between said first pair of electrodes, said means including a circuit for feeding back energy from said second pair of electrodes to said first pair in desired phase to sustain oscillations.

8. In combination, a pair of opposed grid electrodes capable of emitting secondary electrons at a ratio greater than unity, a second pair of opposed electrodes, means for producing an oscillating cloud of electrons between said electrodes, and means for feeding back energy from said second pair of electrodes to said first pair in desired phase to sustain oscillations, said last means comprising a circuit of variable electrical length coupled between each electrode of said second pair and the adjacent electrode of said first pair.

9. In combination, a pair of opposed grid electrodes capable of emitting secondary electronsat a ratio greater than unity, a second pair of opposed electrodes, means for producing an oscillating cloud of electrons between said electrodes including a resonant circuit coupled between said pair of grids, and means for feeding back energy from said second pair of electrodes to said first pair in optimum phase to sustain oscillations.

10. In combination, a pair of opposed electrodes in the form of discs capable of emitting secondary electrons at a ratio greater than unity, an electrode surrounding the periphery of each of said pair of opposed electrodes, means for producing an oscillating cloud of electrons between said opposed electrodes including a tuned circuit coupled between said pair of opposed electrodes, and a tuned circuit coupled between said surrounding electrodes, said tuned circuits being coupled together, whereby a desired phase shift is provided between said electrodes.

11. In combination, a pair of opposed grid electrodes capable of emitting secondary electrons at a ratio greater than unity, a second pair of opposed electrodes, means for producing an oscillating cloud of electrons between said first pair of electrodes including a circuit of variable electrical length between each electrode of said second pair and a grid eleetrofia of said first pair, the space between each electrode of said second pair and the nearer grid ele'ctrbde of said first pair being so chosen that combined with the electrical length of the circuit thzrebetween the electrons passing through said first pair of electrodes at the instant of zero potential thereon arrive at said second pair of electrodes at such time that the potential on said second pair of electrodes is a positive maximum. 1

12. In combination, a hot cathode; means for producing oscillation of electrons emitted therefrom, a first electrode for influencing the amplitude of oscillations, a second electrode capable of emitting secondary electrons at a 'ratio greater than unity and arranged to be impacted by said oscillating electrons, individual tuned circuits connecting said first and second electrodes and said cathode, said circuits being coupled together for the transfer of oscillatory energy therebetween, and means for adjusting the relative phase of the voltages in the circuits of said first and second electrodes.

WALTER VAN B. ROBERTS. 

